Losing gas really quickly?

exiss said:

I'm sorry, but do you mean the dash when you say computer?

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Yes, that is what I mean.

aighead said:

Hold on, you may be missing a setting... You can go into the infotainment screen and change the way the MPG range is read. It behaves very differently depending on how that is set, especially (I assume) if the car is brand new. You can set it to recalculate after each fuel fill up, or you can set it to calculate long term (Trip A/B tripometer). If set to calculate at each fill up your range reader reacts a lot and you'll see a bunch of movement on that range until you drive for a bit, maybe a quarter tank of gas. I'd go into the settings to see where yours is set before you worry too much about it.

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This could be something to check for sure. The average efficiency is constantly updating itself regardless but if you have the trip set to reset on fillup or you are resetting it now and weren't before, you will see it hop all over the place for the first say 25 to 50 miles. After that, it will settle down as the data samples it uses to calculate the average increase to the point where you would have to drive really well or really poorly to start moving the calculated average a whole lot.

frontlinegeek said:

Yes, that is what I mean.



This could be something to check for sure. The average efficiency is constantly updating itself regardless but if you have the trip set to reset on fillup or you are resetting it now and weren't before, you will see it hop all over the place for the first say 25 to 50 miles. After that, it will settle down as the data samples it uses to calculate the average increase to the point where you would have to drive really well or really poorly to start moving the calculated average a whole lot.

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31 is quite normal for our 2.0NA with CVT. The 45 mpg is when you are on the highway and that highway is not hilly and you keep it at or below 70 mph.

My current tank which is about 70/30 City/Highway is clocking in at 31 mpg. I only have about 10k miles more than your car so both are past break-in.

The best way to really know though, is to do as a couple have suggested here and in other threads. Fill the tank, reset your trip counter, run it to the get fuel now light comes on. Note the miles, fill up and do the math. Miles driven divided by gallons filled. You can also gauge the computers guesstimates by noting what the mpg and range is after about 30 miles of mostly continuous city speed driving (Intersection stops only, no idling in yards or parking lots). If that estimated range is the same as the trip counter when your tank is at half (Or even reasonably similar), then you are definitely fine.

It should also be noted that it is not impossible to once in a blue moon, get a bad tank of gas. One or two fill ups of odd behaviour is an anomaly. If it keeps up for 3 or more fill ups and there is no improvement, then maybe there is something going on.

NOTE: When I say fill up, I mean that you ran the tank till the light comes on and THEN fill it up. That way you aren't just prolonging a bad batch of fuel by slowly diluting it with good gas over a long period if you are prone to filling up when you are not closer to empty.

frontlinegeek said:

31 is quite normal for our 2.0NA with CVT. The 45 mpg is when you are on the highway and that highway is not hilly and you keep it at or below 70 mph.

My current tank which is about 70/30 City/Highway is clocking in at 31 mpg. I only have about 10k miles more than your car so both are past break-in.

The best way to really know though, is to do as a couple have suggested here and in other threads. Fill the tank, reset your trip counter, run it to the get fuel now light comes on. Note the miles, fill up and do the math. Miles driven divided by gallons filled. You can also gauge the computers guesstimates by noting what the mpg and range is after about 30 miles of mostly continuous city speed driving (Intersection stops only, no idling in yards or parking lots). If that estimated range is the same as the trip counter when your tank is at half (Or even reasonably similar), then you are definitely fine.

It should also be noted that it is not impossible to once in a blue moon, get a bad tank of gas. One or two fill ups of odd behaviour is an anomaly. If it keeps up for 3 or more fill ups and there is no improvement, then maybe there is something going on.

NOTE: When I say fill up, I mean that you ran the tank till the light comes on and THEN fill it up. That way you aren't just prolonging a bad batch of fuel by slowly diluting it with good gas over a long period if you are prone to filling up when you are not closer to empty.

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I just did this with my last tank of gas on my CTR. My trip computer tells me I'm getting 28.9mpg. I got a range of 271 miles before filling up. 10.313 gallons. Using your math that gives me an actual MPG of 26.27MPG... that's 2.5mpg off of what the car says I get!

frontlinegeek said:

31 is quite normal for our 2.0NA with CVT. The 45 mpg is when you are on the highway and that highway is not hilly and you keep it at or below 70 mph.

My current tank which is about 70/30 City/Highway is clocking in at 31 mpg. I only have about 10k miles more than your car so both are past break-in.

The best way to really know though, is to do as a couple have suggested here and in other threads. Fill the tank, reset your trip counter, run it to the get fuel now light comes on. Note the miles, fill up and do the math. Miles driven divided by gallons filled. You can also gauge the computers guesstimates by noting what the mpg and range is after about 30 miles of mostly continuous city speed driving (Intersection stops only, no idling in yards or parking lots). If that estimated range is the same as the trip counter when your tank is at half (Or even reasonably similar), then you are definitely fine.

It should also be noted that it is not impossible to once in a blue moon, get a bad tank of gas. One or two fill ups of odd behaviour is an anomaly. If it keeps up for 3 or more fill ups and there is no improvement, then maybe there is something going on.

NOTE: When I say fill up, I mean that you ran the tank till the light comes on and THEN fill it up. That way you aren't just prolonging a bad batch of fuel by slowly diluting it with good gas over a long period if you are prone to filling up when you are not closer to empty.

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Just filled my tank so the range miles is at 380 miles. Only been driving for maybe 20ish minutes, and it’s already gone down to 355 miles! Definitely not normal to me since I’ve never experienced this before in the past. But.. I will take what you said into consideration and keep watch. Thanks!

Zeffy94 said:

I just did this with my last tank of gas on my CTR. My trip computer tells me I'm getting 28.9mpg. I got a range of 271 miles before filling up. 10.313 gallons. Using your math that gives me an actual MPG of 26.27MPG... that's 2.5mpg off of what the car says I get!

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So there are several issues going on here...

The misunderstanding of how the trip computers work in the GenX Civics - Contrary to popular opinion, these cars do indeed have a very good idea of how much gas is being used. Your range, however, is dependent on the accuracy of the float in your tank (and the second item I note). This float is affected by all manner of things: What angle your car is at, is the float sticking today, is the float straight up defective, is the float just simply never accurate due to something that happened during assembly or manufacture of the float... But the consumption, THAT is bang on accurate or your car wouldn't work as the engineers know how much go go juice is in the cylinders when it goes bang. Count the squirts, count the RPMs, do some maths, measure the distance travelled... This is not hard math.

The fact that filling up AFTER will always result in a difference of some kind - You don't actually know how much fuel you had in when you were at "full" before you drained and then "filled" up. You could have filled at a pump that cut off when you were at say 11.8 gallons and you aren't one of those people that keeps squeezing in more. Then after driving, you repeat but either at a different pump or even the same and then the pump cuts off at 11.0 or 12.1 because who knows. Literally the only way to know for sure is to have a dedicated fuel cell and go laboratory level testing insane. You only have to have a variance of 0.9 gallons to generate this 10% difference you experienced

Missing what I said - I clearly pointed out that the easiest way to get a feel was to reset the trip and drive till the tank is half empty and see if how far you drove already matches the remaining estimated range. If it is wildly off then there is either something up or you are hot rodding all over the place. Anything less than 5% is statistically irrelevant. Over 10% would for sure be of interest for further investigation.

Without a fuel cell and a whole pile of screwing around, the best you can ever do in the real world is to drive till the light comes on. Stop. Get a known amount of fuel into the car immediately, THEN drive till the light comes on and see how far off the calculations are. The low fuel light is the only thing that you can count on to tell you the same thing every time, provided you trust your fuel level float. Calling back to what I said about your 10% difference, note that even half a gallon difference in what was really going on will exceed 5% variance.

I will say, however, I have no idea how it decides your range right after you fill up. There is some serious chicken's blood and juju going on as far as I can tell. How does it know if I am going on the highway for a whole tank or fixing to get stuck in Boston rush hour traffic? Maybe, if anything, it is using the last trip to decide what to show you. I don't know.

Ducky said:

Pump math is much, much more accurate than the tripmeter.

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Pump math is actually less accurate and less reliable as you don't REALLY know how much fuel you used from the previous fill up. You only know how much you put in during that most recent fill up. "Full" is different every single time you fill up and even a half gallon difference is up to a 5% variance vs what really happened.

And if you read any of the articles that try to claim that the trip computers are wildly wrong, you will find the exact same 5% variance/discrepancy that I speak of shows up in almost all their end user quality testing. 5% is meh. A controlled fuel cell is the only way to actually prove or disprove anything one way or the other.

The only thing that matters in the long run for tracking how your specific car is performing/behaving is that whatever method of measuring/tracking you use, use that and only that as you can't actually compare it to data collected differently.

exiss said:

Just filled my tank so the range miles is at 380 miles. Only been driving for maybe 20ish minutes, and it’s already gone down to 355 miles! Definitely not normal to me since I’ve never experienced this before in the past. But.. I will take what you said into consideration and keep watch. Thanks!

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Same thing has been happening since last October my full tank says 470 or so or whatever miles left when full then when I drive a block down the roads my miles drop to like 445 or so ..most of the time that happens my miles get stuck on 445 even after driving for a while then the computer (I guess it catches itself and then starts counting down normally from that 445). I’ve thought about taking it to the dealership but when I took it in for that grinding noise when accelerating just like most others have been having on their cars the technician said I was crazy and nothing was wrong .

Launcher said:

Same thing has been happening since last October my full tank says 470 or so or whatever miles left when full then when I drive a block down the roads my miles drop to like 445 or so ..most of the time that happens my miles get stuck on 445 even after driving for a while then the computer (I guess it catches itself and then starts counting down normally from that 445). I’ve thought about taking it to the dealership but when I took it in for that grinding noise when accelerating just like most others have been having on their cars the technician said I was crazy and nothing was wrong .

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Right? Has it still been doing that?

exiss said:

Right? Has it still been doing that?

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Yes it still has been doing that .. more towards when I fill up my car’s gas tank ..

Launcher said:

Yes it still has been doing that .. more towards when I fill up my car’s gas tank ..

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Wondering if should I ask the dealer as well.. It's been happening for the last couple weeks so it's a bit worrisome for me.

Launcher said:

Yes it still has been doing that .. more towards when I fill up my car’s gas tank ..

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exiss said:

Wondering if should I ask the dealer as well..

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Ya, Launcher, that sounds like something wrong with the fuel level sender. Maybe you have the same issue exiss. Either way, best to get something like that dealt with before your bumper to bumper coverage is done.

Average mixed driving, the cars should only get 350-370 miles on a "to the light comes on" tank of gas. (Full drain of the tank at 31 mpg is a range of 383 miles. An all highway drive at 43 mpg is a range of 532 miles). If you ARE seeing these distances between fill ups, then something sounds like it is out of whack in your fuel tank.

From the Operator's Manual:

Range -- This estimated distance is based on the vehicle's current fuel economy.

Current fuel economy must be an average but I don't know how it's calculated.

You can fill the tank and see the updated range value.

For example if the new range is 525 miles then the mpg used in the calculation is:

525 / 12.2 gals = 43.0 mpg

Does this number correspond to any of the mpg's shown on the screen? Don't know.

When you're driving in stop and go traffic you can see some big variations in the displayed mpg. If you've just reset the tripmeter you may see some huge swings. If you're getting close to empty and the tripmeter has accumulated several hundred miles the swing in displayed mpg will be much, much smaller.

"If possible, you should always fill the vehicle up before it hits 0. The in-tank fuel pump requires fuel to keep it cool. Running your tank too empty will un-submerge your fuel pump causing it to heat up or, worse for it still, suck up air."

You forget the fuel which is being pumped up through the pump/motor unit. As long as it's pumping it's being cooled and lubricated by the fuel flowing up through it.

If you run it dry and pumping stops then it may overheat.

Fortunately the fuel doesn't get too hot in the tank. On my motorcycle the fuel in the tank gets quite hot from engine heat and radiant heat from the sun.

Electric fuel pumps are very reliable. Just don't leave them in a tank of old gas. The motors are puny and can't overcome residue from old gas.

fjrman said:

Current fuel economy must be an average but I don't know how it's calculated.

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The engines are engineered and the fuel injection volumes are a known quantity. This is not voodoo as not knowing would mean not having the right fuel/air mixture and your car would run like crap. The computer is tracking every single fuel pulse that is injected and that, in lockstep with how far you have driven, will let it calculate your current fuel efficiency. The only guesswork is when trying to guess your current range remaining due to variations in the reading from the fuel level float in the tank. This is also why doing calcs yourself are unpredictable as even half a gallon/2 liters of incorrect measurement will cause as much as a 5% swing in what the car thought you had for range.

Also, our cars definitely do track everything that is injected. If you idle your car or use autostart, your economy ratings will look like garbage.